# Frequently Asked Questions

<!-- TOC -->

- [Frequently Asked Questions](#frequently-asked-questions)
    - [Which Audio Interface / Soundcard is compatible with Aura?](#which-audio-interface--soundcard-is-compatible-with-aura)
    - [ALSA Settings](#alsa-settings)
        - [In the Liquidsoap Logs I get 'Error when starting output output_lineout_0: Failure("Error while setting open_pcm: Device or resource busy")!'. What does it mean?](#in-the-liquidsoap-logs-i-get-error-when-starting-output-output_lineout_0-failureerror-while-setting-open_pcm-device-or-resource-busy-what-does-it-mean)
        - [How can I find the audio device IDs, required for settings in engine.ini?](#how-can-i-find-the-audio-device-ids-required-for-settings-in-engineini)
    - [I have issues with starting the Engine](#i-have-issues-with-starting-the-engine)
    - [I have issues during some Engine play-out](#i-have-issues-during-some-engine-play-out)
    - [Read More](#read-more)

<!-- /TOC -->

## Which Audio Interface / Soundcard is compatible with Aura?

Basically any audio device which is supported by Linux Debian/Ubuntu and has ALSA drivers.
Engine has been tested with following audio interfaces:

- ASUS Xonar DGX,
- Roland Duo-Capture Ex
- Onboard Soundcard (HDA Intel ALC262)
- Native Instruments Komplete Audio 6

## ALSA Settings

### In the Liquidsoap Logs I get 'Error when starting output output_lineout_0: Failure("Error while setting open_pcm: Device or resource busy")!'. What does it mean?

You probably have set a wrong or occupied device ID.


### How can I find the audio device IDs, required for settings in engine.ini?

* **ALSA**: You can get the device numbers or IDs by executing:

    cat /proc/asound/cards

* **Pulse Audio**: You might not need this for Pulse Audio, but still, to see all available devices use:

    pactl list

**If you cannot find correct ALSA settings**  
Well, this is - at least for me - a hard one. I could not manage to find correct ALSA settings for the above mentioned soundcards. The best experience i had with the ASUS Xonar DGX, but still very problematic (especially the first couple of minutes after starting liquidsoap). Since i enabled JACK support i only use that. It is also a bit of trial and error, but works pretty much out of the box.

**If you experience 'hangs' or other artefacts on the output signal**

 * Reduce the quality (especially, when hangs are on the stream) or
 * Check the logs (especially the Liquidsoap logs) for any configuration issues
 * Check ther performance of your computer or audio hardware
 * Install the realtime kernel with

   ```bash
   apt install linux-image-rt-amd64
   reboot
   ```

## I have issues with starting the Engine

**Cannot connect to socketpath /opt/aura/engine/src/liquidsoap/engine.sock. Reason: [Errno 111] Connection refused**

- This indicates some issue with the proper startup of Liquidsoap or any related audio device. Check the Liquidsoap logs for details.

**[clock.wallclock_alsa:2] Error when starting output lineout: Failure("Error while setting open_pcm: No such file or directory")!**

- This might indicate some issue with your ALSA device. Check if `aplay -l` and `aplay -L` returns some valid device(s). You can also try `alsamixer`.
- It might be also helpful to set your default audio device in `/etc/asound.conf`.
- Also check if your user (è.g. `engineuser`) belongs to the group `audio`.
- Check the audio interface configuration section in `engine.ini`. Verify if the default settings `input_device_0="hw:0"` and `output_device_0="hw:0"` are valid device IDs.

## I have issues during some Engine play-out

**Some stuttering sound is hearable. The logs say "strange error flushing buffer ..."**

- Check your Icecast connection. Is it up and running?
- Maybe there is some authentication issue or an Icecast limitation of max clients. See https://github.com/savonet/liquidsoap/issues/524.


## Read More

- [Overview](/README.md)
- [Installation for Development](installation-development.md)
- [Installation for Production](installation-production.md)
- [Running with Docker](running-docker.md)
- [Setup the Audio Store](docs/setup-audio-store.md)
- [Developer Guide](developer-guide.md)
- [Engine Features](engine-features.md)
- [Frequently Asked Questions (FAQ)](docs/frequently-asked-questions.md)